Dynamics of the 5 April 2003 explosive paroxysm observed at Stromboli by a near-vent thermal, seismic and infrasonic array

On 5 April 2003 an array of thermal, infrasonic and seismic sensors tracked the dynamics of a major explosive ( paroxysmal) event at Stromboli. The thermal signal recorded a decline similar to 1 hour before the paroxysm, which itself lasted 6.5 minutes and opened with a similar to 14 s low thermal amplitude phase. This was followed by three main explosive phases, with gas and ejecta velocities of 324 and 185 m/s being calculated for the first phase. The delay time between thermal and infrasonic signals indicates a very shallow (< 150 m) source for fragmentation. A strong tilt component in the seismic signals shows that the conduit began to expand at least 90 s before the explosion. Large seismic amplitudes were recorded during the emission onset. The seismic signal can thus be related to stress build up followed by release during the ejection of the gas-particles mixture. We calculate that the cloud of hot gas and ash emitted during the explosion had an overpressure of 3.8 MPa and involved 5.7 x 10(5) m(3) (2.9 x 10(6) kg) of gas.